Background: Synovectomy specimens represent important material submitted from the orthopedist to the pathologist. However, no consistent histopathological grading system for chronic synovitis has been established so far.
Patients and methods: The three compartments of chronic synovitis (enlargement of lining cell layer, density of synovial stroma cells, leukocytic infiltrate) are graded semiquantitatively (from 0=absent to 3=strong), and the points for each compartment add up to the synovitis score: 0-1 = no synovitis, 2-4 = low-grade synovitis, 5-9 = high-grade synovitis. A total of 618 synovial specimens (resections n=559, biopsies n=59) from degenerative and inflammatory joint diseases were graded by two independent observers.
Results: Median synovitis scores when correlated to clinical diagnoses were: 1, control; 2, osteoarthritis and post-traumatic arthritis; 3, psoriatic arthritis; 5, reactive and rheumatoid arthritis. The differences between rheumatic and non-rheumatic diseases were significant (p<0.001). The correlation between the two observers was high (p<0.001).
Conclusions: The proposed synovitis score enables stratification of chronic synovitis into low-grade (score 2-4) and high-grade (score >4), which is correlated to the nature of the disease (low-grade to non-rheumatic, high-grade to rheumatic), and it therefore contributes to the diagnosis of rheumatic and non-rheumatic joint diseases.